The present invention relates to a booster for a handy phone and more particularly to a booster for amplifying the transmission output of a handy phone.
Handy phones in general are limited in battery capacity and heat radiation structure for implementing a light weight configuration and attractive appearance. Therefore, a transmission output available with a handy phone is smaller than the transmission output of a fixed communication apparatus. To increase the transmission output of a handy phone, it is a common practice to connect an exclusive booster to the phone. However, should the booster be simply connected to the handy phone, it would obstruct ventilation and would thereby generate excessive heat.
Japanese Patent Publication No. 3-20167, for example, discloses a device constructed to reduce the heat generation of a handy phone. The device includes a detecting circuit responsive to the connection of an exclusive booster to a handy phone. An automatic output power control circuit controls the transmission power of the phone to a preselected value relating to a reference voltage. The output of the detecting circuit is fed to a reference voltage generator included in the automatic output power control circuit for generating the above reference voltage, thereby varying the reference voltage. As a result, the output power of the phone is lowered to the minimum input necessary for the booster.
The device taught in the above document has some problems left unsolved, as follows. The device is not operable without the detecting circuit responsive to the connection of the booster to the phone. The detecting circuit needs extra connection lines because the connection of the booster to the phone is usually implemented by physical connection lines.
Assume that transmission power to be output from the booster changes when the booster is connected to the phone. Then, the class of a transmitter included in the phone and usually stored in the phone in relation to its identification must be changed from one provided when the phone is used alone. In addition, such a condition must be reported to a base station by using the replaced class. However, such information is not necessary when it comes to a booster applicable to a cellular system because the output power of the booster does not have to be changed from the original output power of the phone, i.e., the class of a transmitter does not have to be changed.
Further, the above detecting circuit will probably differ from one manufacturer to another manufacturer. It will therefore be difficult to connect devices put on the market by different manufacturers.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 4-361430, 7-336243, 7-226710, and 8-195712.
It is therefore an object of the present invention to provide a booster for a handy phone eliminating the need for extra connection lines.
It is another object of the present invention to provide a booster connectable to any kind of handy phone.
A booster for a handy phone of the present invention includes a variable gain power amplifier for amplifying the power of a transmission wave output from the phone to which the booster is connected. A splitting section splits the transmission wave with the amplified power output from the variable gain power amplifier into two. A decoder decodes a particular transmission message included in the transmission wave split by the splitting section and determining transmission power to thereby output a reference signal matching in level with the transmission power. A detector detects the transmission wave with the amplified power output from the variable gain power amplifier. A controller compares the level of the reference signal output from the decoder and the level of a detected signal output from the detector and variably controls the gain of the variable gain power amplifier such that the reference signal and detected signal coincide with each other. A transmitting section transmits the transmission wave output from the splitting section by radio.